Here is a simple programmable load. It’s basically a constant current sink that is controlled through a pot. The current is sunk through a high power FET which needs to be cooled to function properly – [via]

Here’s a link to a *really* simple linear constant current sink i put together

This design is about as simple as it gets. . .multi-turn pot controlled and readout done by a voltmeter:) The good news is that it works quite well for moderate loads. It was put together to regulate current flowing through a copper electroplating tank. Due to the monstrous Pentium II (or maybe III?) heat sink, it isn’t noticeably warm when eating 9A of current.